This invention relates to novel hydrocarbon conversion catalysts, methods for their preparation, and use thereof in hydrocarbon conversion processes. More particularly, the present invention relates to a catalytic cracking catalyst suitable for the conversion of heavy hydrocarbon feeds, for example residua, which catalyst is tolerant of contaminating metals often found in such feeds.
The refining industry today emphasizes not only the gasoline yield of a hydroconversion process, but also the gasoline quality obtainable by that process, particularly its octane. In the United States, the fluid catalytic cracking (FCC) process provides about 35% of the gasoline pool. Consequently, refiners are very interested in boosting the octane of the product coming from these type units. Several factors affect the gasoline yield and quality produced by an FCC unit. Feedstock type, catalyst type, and process variables, in particular, temperature and pressure, are among the major factors affecting octane of the gasoline.
Catalytic cracking systems ordinarily employ catalyst in a moving or fluidized bed. Catalytic cracking is also carried out in the absence of externally supplied molecular hydrogen, and is, for that reason, distinctly different from hydrocracking, in which molecular hydrogen is added in processing. In catalytic cracking, an inventory of particulate of particulate catalyst is continuously cycled between a cracking reactor and a catalyst regenerator. In a fluidized catalytic cracking (FCC) system, a stream of hydrocarbon feed is contacted with fluidized catalyst particles in a hydrocarbon cracking zone, or reactor, at a temperature of about 425.degree.-600.degree. C. The reactions of hydrocarbons in the hydrocarbon stream at the elevated operating temperature result in deposition of carbonaceous coke on the catalyst particles. The resulting hydrocarbon products are separated from the coke-deactivated, spent catalyst and are withdrawn from the reactor. The coked catalyst particles are stripped of volatiles, usually by means of steam, and passed to the catalyst regeneration zone. In the catalyst regenerator, the coked catalyst is contacted with oxygen. The coke is burned off the catalyst, restoring catalytic activity and simultaneously heating the catalyst to between 540.degree. and 815.degree. C. Flue gas formed by combustion of coke in the catalyst regenerator may be treated for removal of particulates and conversion of carbon monoxide, after which it is normally discharged into the atmosphere.
In ordinary catalytic cracking processes, various metallic contaminants which may be present in the hydrocarbonaceous feedstock, particularly vanadium, nickel and iron, cause the degradation and/or deactivation of the catalytic cracking catalyst. Particularly susceptible to vanadium contamination are crystalline aluminosilicate zeolites, either natural or synthetic. This deactivation causes distillate yield loss, particularly through loss of active acid cracking sites, as well as metal poisoning via secondary dehydrogenation and coking reactions caused by the deposition of these heavy metals on the catalyst. Remedial technology has evolved in various ways to deal with this metals-contaminant problem. One mechanism which has evolved includes the use of various diluents as metals passivators or traps, which contain materials which will chemically combine with and effectively tie up the offending materials. These traps have proved particularly effective with regard to vanadium. These traps may be present on a single particle with the cracking catalyst or they may be employed on a separate discrete component of a dual particle catalyst system.
In general, then, prior art zeolite catalysts show a tremendous activity advantage, and good gasoline selectivity. Unfortunately, they continue to demonstrate higher hydrogen-transfer activity which reduces the olefinic character of this gasoline, thereby reducing the octane rating. They are also significantly susceptible to deactivation or other contamination by heavy metals, especially vanadium. It would be beneficial to have a catalyst which achieved both good conversion and good selectivity to gasoline with a high octane rating for vacuum gas oil (VGO), as well as contained metals passivation or trap components, for feeds such as residua and residua blends, which contain contaminating metals. The present invention seeks to provide an FCC catalyst that is vanadium tolerant and provides high octane gasoline.